1. Field of the Invention
The present invention relates to a method for producing a commutator ring for a commutator of an electric machine, as well as an electric machine.
2. Description of Related Art
Methods of the type mentioned at the outset for producing so-called roll commutators are known from published German patent application documents DE 195 43 998 A1 and DE 197 43 086 A1. In this method, a previously stamped continuous loop provided with a desired profile and made of copper or another electrically conductive deformable material is notched transversely to its direction of motion, to form the lamellae that are connected by a small crosspiece to the adjacent lamellae, and, in the commutator from published German patent application document DE 195 43 998 A1, have a plurality of swallow-tail-shaped recesses running in the longitudinal direction of the tape. A desired number of lamellae is cut off from the continuous loop that was thus reformed, and is closed by rolling using a rolling tool to form a commutator ring.
Into the closed commutator ring a hollow cylindrical carrier is subsequently introduced in such a way that it is aligned coaxially to the commutator ring, and then the interspace between the inner circumference of the commutator ring and the outer circumference of the carrier has a free-flowing insulating compound poured into it, which fills the swallow tail-shaped recesses that encircle the inner circumference of the commutator ring and the axial notches between the lamellae, and hardens after being poured, to produce a reliable, form locking connection between the carrier and the commutator ring, and to insulate electrically the adjacent lamellae at the contact surface of the carbon brushes from one another.
Since the electric machine equipped with the commutator is able to rotate in operation at a speed of up to 30,000 revolutions per minute, the commutator ring is subject to strong centrifugal forces which, barring suitable countermeasures, could lead to an undesired deformation of the metallic commutator ring, and with that, possibly to increasing spark formation between the carbon brushes and the commutator. To counter this, it is already known, among other things, from published German patent application document DE 103 19 460 A1, that one may provide the end faces of the lamellae with groove-like recesses, which are reached through by a prestressable ring armature, which holds each individual lamella radially inwards towards the carrier of the commutator ring in a prestressed manner. Because of this, at least the end faces of the commutator lamellae are prevented from detaching radially outwards from the carrier or from the insulating compound, at high operating speeds of the commutator. However, in order to avoid imbalances, the ring armature should be developed to be rotationally symmetrical, which makes the construction of prestressable ring armatures from high-tensile, nonelastic materials considerably more difficult. In addition, the processing and mounting of prestressable ring armatures in the commutator ring is also relatively costly.